The present invention relates to heatpsreaders having pressure sensitive adhesive, and more particularly an improved/enhanced lamination process between the heatspreader and pressure sensitive adhesive resulting in a void free interface.
In the last few decades, the electronics industry has literally transformed the world. Electronic products are used by, or affect the daily lives of, a large segment of the world's population. For example, telephones, television, radios, Personal Computers (PCs), laptop PCs, palmtop PCs, PCs with built-in portable phones, cellular phones, wireless phones, pagers, modems, and video camcorders, are just a few of the electronic products that have been developed in recent years and which have been made smaller and more compact, while providing more and/or enhanced functions than ever before.
The amount of heat generated by an integrated circuit (IC) die is related to the number of transistors on the IC die and the clock speeds at which they operate. The faster the transistors on the IC die are operated, the more heat is generated. Since advances in IC fabrication technology continue to make possible both increased transistor density and higher clock speeds, the problem of heat generation is becoming increasingly severe, particularly in high performance IC dies, which push the limits of fabrication technology.
As an increasing amount of heat is generated by the IC dies, the junction temperatures of the transistors in the device increases proportionately. The failure of the semiconductor device is directly related to the junction temperature at which it is operated. The higher the junction temperature, the higher the failure rate. A very significant limitation of the operation and reliability of the IC package is the efficient extraction of the generated heat from the IC die.
It is generally known to provide a heatspreader or a heat sink for an IC die in order to transfer the generated heat away from the IC die itself and into the surrounding air, thus reducing the junction temperature. The heatspreader is generally located as physically close to the IC die as possible in order to maximize the amount of heat transferred. Heatspreaders typically are constructed from a high thermal conductivity material and are designed to present a maximum amount of surface area to the ambient air in order to allow the heat generated by the IC die to be removed, either by natural or forced convection.
As more and more transistors are fabricated on the IC die, the overall amount of heat generated is increased. By using a flip-chip package, the active surface of the IC die is flipped and the non-active surface of the IC die is available to provide a direct connection between the IC die and the heatspreader. The heatspreader is attached to the non-active surface of the IC die with an adhesive or epoxy. Although thermal performance is improved, this direct connection suffers from several disadvantages. The major concern is the debonding or delamination of the heatspreader and IC die at the interface.
FIGS. 1a, 1b and 1c show the present method of attaching a pressure sensitive adhesive (PSA) to the heatspreader. The PSA assembly consists of a PSA 10 with a polyester release liner 15 applied to each side (FIG. 1a). Prior to attachment to the heatspreader 25, one of the liners 15 is removed exposing the adhesive (FIG. 1b). The PSA 10 is then attached to the heatspreader 25 with finger pressure, to tack them together. The assembly is then transferred to a fixture 20 in a press, which may be pneumatic, to supply the joining force. Force is applied to the assembly by the press, in the direction of arrow 30, joining the heatspreader 25 and PSA 10, as shown in FIG. 1c.
After the joining process of the PSA 10 to the heatspreader 25, the interface between them contains trapped air bubbles and voids 35 that tend to prohibit good adhesive contact between the heatspreader 25 and PSA 10. To compensate for this, excessive force is often applied to the assembly in order to try to achieve good contact between the components, which may damage them. These voids and trapped air 35 are often the root cause of delamination between the heatspreader and the IC package during assembly and use. This is due to the fact that after the heatspreader 25 is attached to the IC die of a flip-chip package, the assembly is heated to elevated temperatures for solder ball attachment to a printed circuit board. The trapped air 35 at the interface between the heatspreader 25 and the PSA layer 10 will cause moisture to outgas at the elevated temperature during subsequent process steps and use. This outgassing may cause delamination at the adhesive interface 10 between the heatspreader 25 and the IC die (not shown). If the adhesive interface 10 does not delaminate, there is still a high probability that the package will fail post solder ball attachment due to warpage and heat generated during use.
As the semiconductor technology advances, the need for heat dissipation remains critical. Thus, the attachment of the heatspreader to the IC die becomes increasingly important to device performance. In view of the above, it is evident that what is needed is an improved technique and method of adhesive attachment to the heatspreader of the semiconductor package that decreases debonding and delamination resulting from air trapped in the adhesive layer interface.